Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$44.29	10.445%	$48.9161	$48.92	$48.90	$48.90
Purchase #2	$30.50	6.257%	$32.4084	$32.41	$32.40	$32.40
Purchase #3	$94.38	6.422%	$100.4411	$100.44	$100.45	$100.40
Purchase #4	$180.82	9.489%	$197.978	$197.98	$198.00	$198.00
Purchase #5	$174.75	5.728%	$184.7597	$184.76	$184.75	$184.80
Purchase #6	$48.88	9.186%	$53.3701	$53.37	$53.35	$53.40
Purchase #7	$63.48	11.199%	$70.5891	$70.59	$70.60	$70.60
7 purchase totals =	$637.10		$688.4625	$688.47	$688.45	$688.50